The present invention relates to a method of limiting coupling losses between a monomode optical fiber having a mode diameter of W.sub.o, and an optical system having a mode diameter W'.sub.o that is different from W.sub.o.
It is recalled that the mode radius W.sub.o of an optical fiber may be defined as follows: ##EQU1##
Typically, a monomode optical fiber has a core diameter in the range about 8 .mu.m to about 10 .mu.m, and a cladding outside diameter of about 125 .mu.m. The index difference .delta.n can lie in the range 5.times.10.sup.-3 to 50.times.10.sup.-3. The usual value lies in the range 5.times.10.sup.-3 to 16.times.10.sup.-3.
It is extremely difficult to couple such a fiber, and in particular to couple it to a laser diode. In order to achieve optimum coupling, two conditions must be met:
an optical surface having a radius of curvature that is extremely small and therefore very difficult to achieve must be provided at the end of the fiber; and PA1 said optical surface must be disposed almost touching the diode, and this is mechanically impossible. PA1 Currently, the coupling percentage does not exceed 45% to 50%.
The problem is to create means for providing a better coupling percentage in spite of a distance that is mechanically acceptable being maintained between the diode and the fiber, and tolerances that are feasible being maintained for the angular position of the fiber relative to the diode.